Many kinds of removable band-type couplings for pipes exist in the art. It is noted that throughout the specification and claims, the term “pipe” encompasses any kind of generally cylindrical object.
Such couplings have an elastomeric seal assembly which is tightened to form a watertight seal against the pipe. Couplings are known that can be used for a range of pipe diameters. Generally, such seal assemblies have two layers of gaskets (seals), for example, constructed of a first ring seal seated over a second ring seal. The seals can be easily disconnected from one another to allow sealing against different diameter pipes. For smaller diameter pipes, both the first and second ring seals are used; for larger diameters, only one seal is used.
A prior art seal 1 of this type is shown in FIG. 1. Seal 1 includes an outer sealing layer 2 connected to an inner sealing layer 3 with mating portions that include annular ridges 4 that are received in annular grooves 5. The annular ridges 4 and annular grooves 5 have a trapezoidal or triangular cross-section. There is a mating clearance between annular ridges 4 and annular grooves 5 to facilitate mating the two portions together. It has been found that such a mating structure has limited ability to withstand forces due to fluid pressures in the assembled coupling with liquid flowing through the coupling. The fluid pressures can cause the two sealing layers 2 and 3 to separate from one another (in the radial directions of arrows 6 and 7), and/or in the axial direction (arrow 8) along the slant of the trapezoidal or triangular surface, at different circumferential portions of the sealing layers.